The present invention relates to a vein filter for preventing pulmonary infarction and which is mainly indwelt in the inferior caval vein.
Recently, as the number of elderly persons of advanced age has increased in society, more attention has been paid to an increase in vein diseases as well as to an increase in arterial sclerosis. Vein diseases have not been given as much importance as arterial diseases. However, high attention has recently come to be paid to their importance. This is because when deep vein thrombosis occurs, a part of it is released and flows into the pulmonary artery to induce thromboembolism of the pulmonary artery, and as a result severe respiratory failure is caused. Once pulmonary artery thromboembolism occurs, the prognosis in many cases is very poor and there is a high risk of death unless an effective therapeutic means is applied.
Therefore, to forestall pulmonary artery thromboembolism, a vein filter has been indwelt in the inferior caval vein in order to collect chyme blood or thrombi, which occurs on the side of the lower extremities. However, conventional filters having wires constructed in the form of a framework of an umbrella which can open in a conical shape have the problem that since the respective wires are not restricted and move freely, the distances between adjacent wires are not always the same, with the result that a broad gap may be formed between wires and chyme blood or thrombi cannot be sufficiently collected. Another problem is that the distances between adjacent wires may be uneven and cause the conical shape to deform. This results in the filter tending to be indwelt in the vein obliquely and unstably so that it tends to move toward the proximal portion of the inferior caval vein and is difficult to maintain in a predetermined position. Furthermore, it is difficult to adjust the pressure at which the wires contact the inner wall of the vein and problems occurs in that too strong a pressure results in constriction or injury of the inner wall and too weak a pressure fails to give stable anchorage.
Accordingly, in view of the above problems of the prior art, the present inventors have made extensive research with respect to a vein filter in which the distances between wires are made equivalent to increase the collectability of chyme blood or thrombi and to improve the stability of the filter when indwelt and as a result they have achieved the present invention.
The present invention is a vein filter which comprises a head member, at least three wires of equivalent length, the wires having front ends fixed to the head member, the wires extending radially from the head member backward, a connection part comprising threads of substantially equivalent length, each connecting two adjacent wires at a position an equivalent distance from the head member, and a hook part provided on the connection part for hooking onto an inner wall of a blood vessel to fix the filter.
Further, the present invention is a vein filter which further comprises a shaft having a front end at which the head member is provided and a slide member slidable along the shaft, wherein the wires have rear ends connected to the slide member.
Furthermore, the present invention is a vein filter in which the wires comprise a shape memory alloy or a stainless spring steel.